PARENT SESSION

2A - Mixture Toxicity
Hall 6
8:30 AM - 12:30 PM, Monday, 28 April 2003
Chair: Hermens, J.¹, ¹
Co-chair: Toy, R.², Backhaus, T.³, ^{2 3}

(MO6/6) What contributes to the combined effect o a realistic mixture?

Walter, Helge¹, Grote, Matthias¹, Brack, Werner¹, Scholze, Martin², Altenburger, Rolf¹, ¹ Centre for Environmental Research Leipzig-Halle GmbH, Leipzig, Saxony, Germany² University of Bremen, Bremen, Bremen, Germany

ABSTRACT- For the assessment and prediction of the toxicity of chemical mixtures, the concept of CONCENTRATION ADDITION (CA) and the concept of INDEPENDENT ACTION (IA) are proposed. The accuracy of the prediction and the assessment of the combined effect of a mixture depends on various factors. The ratio at which the components are composed to a mixture is of special relevance, as it determines which components contribute to the combined effect of the mixture and to what extent. So far reference mixtures could be established, demonstrating the capability of both concepts to predict and assess combined effects. The components of these mixtures were composed in proportion to their relative toxicity as single compounds to provide for equitoxic contributions to the overall effect. In contrast, environmental exposure situations are often characterised by chemicals occurring at non-equitoxic ratios. This provokes the question, whether for such more realistic mixtures the expectation of a combined effect is plausible? If so, is there a background of components, irrelevant for the observed and the predicted mixture effect? In this study, biological and chemical methods were applied to identify pollutants for mixture experiments with ecotoxicological potency in sediments from a contaminated site. The chemicals were experimentally investigated individually and composed to a mixture at different ratios. Based on the toxicity information of all identified toxicants and of the major toxicants, expectations of the mixture toxicity were calculated and were compared with experimental results. The applicability of the concepts of CA and IA to assess the toxicity of mixtures of environmental chemicals will be discussed with respect to the relevance of the mixture ratio and background mixtures.

Key words: Joint action, Mixture toxicity, Algae biotest, Effect-orientated fractionation